Current research suggests that high intake of saturated fat increases the risk of cardiovascular disease and cancer, and feeding polyunsaturated fatty acids decreases plasma lipid values. However, our understanding of the roles of specific types of fatty acids in nutrition and health remains limited. This is primarily because the technology for analysis of fatty acid compositions in human tissue has only recently achieved the required specificities and secondarily because application of the technology on the large scale of an epidemiologic study has had to await recent advances in automation of the chromatography. Also intervention studies, aimed at reducing dietary intake of PUFA for long periods of time, are either impractical or unethical. We propose to study the absolute concentrations and percents of fatty acids in 480 plasma specimens from an age and sex stratified random sample of subjects in the Framingham Offspring Study. The primary goals are: (1) to calculate the prevailing distribution of fatty acids in the general population; and (2) to study the interrelationships among levels of fatty acids, in particular w3 and w6 fatty acids, with lipoproteins and apolipoproteins. Secondary goals include exploration of relationships among fatty acid compositions of different lipid fractions and evaluating their relationships with various cardiovascular risk factors. Over 60 fatty acids will be quantitated using capillary gas-liquid chromatography supported by state-of-the-art data acquisition. Tables of reference values will be produced for the general population and for selected subpopulations. Multivariate methods of statistical analysis will be employed to explore correlations among fatty acids and other biochemical markers. This study may confirm preliminary results that suggest greater prevalence of low levels of EFA, particularly w3 fatty acids, among people with cardiovascular disease and hypertension, and would provide further confirmatory evidence to our results that hyperlipidemia is inversely associated with essential fatty acid levels.